In a wireless communication system it is often desirable to locate users who are making calls. Applications for such a technology would include 911-emergency services, so that police/fire/ambulance services could be dispatched to a user making a call. Other applications would include fraud detection, police investigations, and the like.
Previously installed cellular systems had little capability in this regard. For example, in AMPS (Advanced Mobile Phone System) Cellular Radio, a user could be located within a cell by determining which base station antenna was used to serve the user. However a cell could be as large as 3-5 miles in radius, making this information practically useless. Since many of the dense urban cell sites are now much smaller, and many of the urban/suburban cell sites are now sectorized, using sectored antennas to limit a channel's service area to just one sector of a cell, the coverage areas of a cell are now smaller. However, the area even in these smaller cells can still be more than one square mile. This still makes locating a user impractical for most purposes. Other radio systems, like US Digital Cellular (USDC) and Group Speciale Mobile (GSM) use the same method of identifying the cell or sector, and thus could do no better than the AMPS system.
While there are other location alternatives, such as the use of Global Positioning System (GPS) units at the subscriber unit, or triangulation onto a transmitting subscriber unit, these and similar approaches are too costly to be used by most subscribers, or in the case of triangulation, require other costly and time-consuming resources to be dedicated.
There remains therefore a need for an improved, cost-efficient approach for locating subscribers in a wireless communication system.